An electrical interface in an electronic device, such as a personal computer and a server, is now shifting from a parallel interface to a serial interface. In the serial interface, a stable transmission waveform is needed for using a high-frequency band. Therefore, it is needed to appropriately detect transmission path loss, jitter, noise, and characteristic variations (production variations) caused by production etc., and to control a communication circuit based on the detection.
A pulse discrimination degradation detection system is proposed in which a communication apparatus detects a state of degrading factors related to an occurrence of a code error, and transmits the state to an opposing communication apparatus to thereby detect the degrading factors in a remote location (refer to Patent Document 1).
A transmission signal equalization system is also proposed in which a reception circuit detects an equalization characteristic based on a reception signal that has passed through a reception path, and calculates a difference between the equalization characteristic and an optimal equalization characteristic, and in which a transmission circuit controls the equalization characteristic based on the difference (refer to Patent Document 2).
Patent Document 1 Japanese Laid-Open Patent Publication No. 64-016048 Patent Document 2 Japanese Laid-Open Patent Publication No. 2004-356780
As illustrated in FIG. 10, an electrical interface includes, for example, a transmission LSI 102 that transmits a signal (waveform), a transmission path which is formed by a printed circuit board 101 and a connector (or cable) 106, and a reception LSI 102 that receives a signal. In designing such the electrical interface, it is needed for obtaining optimal transmission quality to take into consideration performance of transmission and reception (a transmission unit 103 and a reception unit 104), characteristic variations of elements and materials, characteristics of elements which form the transmission path, noise, etc. In this case, examples of items is to be taken into consideration include, for example, transmission performance; reception performance; production variations in LSI, materials, and characteristics; power supply noise; crosstalk noise; reflection; and signal loss at wires and connection parts of printed circuit board, cables, connectors, and transmission LSI and reception LSI.
The loss and the jitter can be obtained by calculation. Further, a model is created in advance which takes the elements, noise, production variations, etc. into consideration, and pre-analysis of the transmission waveform is performed by setting an amplitude, an emphasis characteristic (emphasis), and the equalization characteristic to various values using the model. Based on the calculation or the pre-analysis, the electronic device is designed so that the loss and the jitter do not exceed determined values. Subsequently, in an evaluation of the electronic device, the amplitude, the emphasis characteristic, and the equalization characteristic are manually set to obtain an optimal transmission waveform or optimal transmission quality. As a result, the optimal amplitude, optimal emphasis characteristic, and optimal equalization characteristic can be obtained for the electronic device, and these obtained values can be set to the electronic device.
However, in mass-produced electronic devices (mass production devices), influence of the production variations is more apparent than in prototype electronic devices. More specifically, characteristics of the mass production devices are different device by device, and cannot be uniformly optimized. Therefore, the amplitude, the emphasis characteristic, and the equalization characteristic obtained by evaluating the electronic device before the mass production are not necessarily optimal. Furthermore, there are many factors of the production variations, so that it is significantly difficult to take all factors into consideration to optimize the amplitude, the emphasis characteristic, and the equalization characteristic of the transmission LSI and reception LSI.
Therefore, in practice, the amplitude, it is needed to set the emphasis characteristic, and the equalization characteristic for each mass production device in a test of the mass production devices at shipping time. As a result, enormous man-hours are required to ship the mass production devices.